Along with the development of science and technology, the electronic expansion valve has been commonly used in the field of inverter air conditioners. It is a step motor electronic expansion valve that is generally used in the field of air conditioners. The electronic expansion valve comprises a step motor and a valve body, and the opening of the valve body is controlled by the rotation of the step motor. The driving circuit of the step motor is connected with the step motor through a drive wire. When the electronic expansion valve is to be driven, the controller sends a pulse control signal to the driving circuit to thereby drive the step motor to rotate to make the valve body reach a corresponding opening.
However, at present, the application of the electronic expansion valve in the field of inverter air conditioners mainly relates to the technique of how to control the rotation of the step motor according to the change of the temperature and pressure to thereby adjust the opening of the valve body of the electronic expansion valve. In the use of the electronic expansion valve in the prior art, the pressure and temperature are sampled by a temperature and pressure sensor, and the target opening of the electronic expansion valve is controlled based on the collected pressure and temperature and according to a control algorithm. The CPU obtains the opening desired by the electronic expansion valve by calculation and converts it into a corresponding pulse signal, which drives the step motor of the electronic expansion valve by a driver, and the step motor drives the valve body to rotate to thereby adjust the opening of the electronic expansion valve. As mentioned above, many mature techniques, which are not greatly different, are existing in terms of the macro-control of the valve body opening of the electronic expansion valve, but few of them relate to the control details of the electronic expansion valve, i.e., the drive technique of starting and stopping the electronic expansion valve itself. Due to the overlook in terms of the control details, that the drive is out of step generally appears in the electronic expansion valve in use, and the electronic expansion valve cannot be effectively driven and cannot effectively keep the current opening and the like.
Especially, the control manner of the start of the electronic expansion valve in the prior art is as follows: after the electronic expansion valve was stopped last time, and when the target pulse signal changes, the electronic expansion valve is directly turned on and off at a normal operating rate directly from the current pulse signal. There is not anything wrong in such drive manner of the electronic expansion valve in normal circumstances. However, there are two circumstances that will render the electronic expansion valve unable to effectively act. The first circumstance is that when the electronic expansion valve has not been used over a long period of time or there is oil or a foreign matter adhered or blocked in the valve body, the electronic expansion valve generally cannot be effectively driven due to an insufficient starting torque of the motor, which causes a case of slip and step-out, so that the electronic expansion valve cannot be effectively turned on and off. The second circumstance is that after the stop of the motor of the electronic expansion valve, a current is applied to the stop pulse signal of the electronic expansion valve, thereby making the magnetic field between the stator and the rotor of the motor of the electronic expansion valve form a holding torque, so that the coil of the electronic expansion valve still keeps the rotor in a state when it is stopped in the case of not being electrified. However, in actual circumstances, under the impact of the refrigerant pressure and the like, the rotor of the motor of the electronic expansion valve will be inevitably displaced. The start is performed according to the pulse position where the electronic expansion valve was stopped last time in the case that the rotor is displaced, and the case that the start is out of step is generally caused due to the deviation of the position of the rotor.
In addition, the control manner of the stop of the electronic expansion valve in the prior art is as follows: generally, after the electronic expansion valve operates to reach the target pulse, a current of 50 ms or more is further continuously applied to the electronic expansion valve to increase the holding torque of the electronic expansion valve to prevent the S pole or the N pole of the rotor magnetic field of the motor of the electronic expansion valve from being misplaced from the N pole or S pole of the stator magnetic field. However, in actual circumstances, it still hardly ensure that the S pole or the N pole of the rotor magnetic field of the motor of the electronic expansion valve is not misplaced from the N pole or S pole of the stator magnetic field only by further continuously applying a current of 50 milliseconds or more to the electronic expansion valve after the electronic expansion valve operates to reach the target pulse.
Thus, the drive technique of starting and stopping the electronic expansion valve in the prior art still hardly overcome the defect that the electronic expansion valve cannot be effectively driven due to an insufficient starting torque of the motor and the defect that the start is out of step due to the deviation of the relative position between the rotor and the stator, and cannot ensure that the valve body opening of the electronic expansion valve is correctly controlled. However, in the field of inverter air conditioners, especially in the field of commercial inverter-driven multi-split air conditioners, the opening of the electronic expansion valve has an irreplaceable function on the control of the entire air conditioning system. Thus, whether or not the electronic expansion valve can be correctly turned on, whether or not the opening is proper and whether or not the current opening can be kept decide the performance and reliability of the air conditioning system. And in order obtain a good performance and reliability, the drive technique capable of correctly driving the electronic expansion valve is the key as for whether or not a product of an air conditioning system is successful.
Thus, there exists a need for a technique capable of effectively controlling the start and stop of the electronic expansion valve to ensure that the valve body opening of the electronic expansion valve is correct.